Control system for electrostatic precipitator



July 18, 1961 w. a. JARVINEN CONTROL SYSTEM FOR ELECTROSTATIC PRECIPITATOR Filed April 3, 1958 3 Sheets-Sheet 1 PREC/P/T/ITOR INTEGR/ITO/P /N T56R14 TOR P0 WER SUPPL Y Fig.2.

Inventor:

Willard B. Jarvinen, bgfl I IS Attorney.

July 18, 1961 w. B. JARVINEN 2,992,699

CONTROL SYSTEM FOP. ELECTROSTATIC PRECIPITATOR Filed April 5, 1958 3 Sheets-Sheet 2 2f 5 F733.

P0 WER SUPPL Y Inventov: illard B. Jarvifieh,

b is At orneg.

July 18, 1961 CONTROL SYSTEM FOR ELECTROSTATIC PRECIPITATOR Filed April 3, 1958 W. B. JARVINEN Fig.5:

3 Sheets-Sheet 3 is Atfiorneg.

United States Patent 2,992,699 (IONTROL SYSTEM FOR ELECTROSTATIC PRECIPITATOR Willard B. Jarvinen, Roanoke, Va.., assignor to General Electric Company, a corporation of New York Filed Apr. 3, 1958, Ser. No. 726,179 11 Claims. (Cl. 1837) This invention relates to control systems, more particularly to control systems for controlling the voltages applied to the electrodes of electrostatic precipitators, and it has for an object the provision of a simple, reliable, improved and inexpensive system of this character.

The efiiciency of operation of a precipitator is dependent on the rate of interelectrode sparking, and accordingly a further object of this invention is the provision of a control system in which the voltage applied to the precipitator electrodes is controlled by the time integral of voltage signals each of which is representative of an interelectrode spark.

A corollary object of the invention is the provision of a precipitator control system embodying an integrator for producing a direct output voltage which is representative of the time integral of an input voltage. A further object of the invention is the provision of a precipitator control system in which correction of the electrode voltage is effected in a series of steps separated from each other by time intervals.

In carrying the invention into effect in one form thereof, a voltage-varying device is included in the supply connections to the precipitator electrodes and a sparksensing device is provided together with an integrating device for producing a direct output voltage changing in magnitude at a predetermined rate and having a polarity related to the sparking rate. Means responsive to the output voltage of the integrating device are provided for controlling the voltage-varying means to adjust the voltage supplied to the electrodes in a sense which is related to the polarity of the output voltage and to a value which will result in interelect-rode sparking at an optimum predetermined rate.

For a better and more complete understanding of the invention, reference should now be had to the following specification and to the accompanying drawings of which FIG. 1 is a simple schematic sketch in conventional block diagram form of an embodiment of the invention. FIG. 2 is a simple elementary diagram of a spark-sensing or detecting device which may be utilized in the system of FIG. 1. FIG. 3 is a simple elementary diagram of an integrating device which appropriately may be utilized in the system of FIG. 1. FIG. 4 is a simple elementary diagram of a modified form of integrating device which may be utilized in the system of FIG. 1 in combination with the integrating device of FIG. 3. FIG. 5 is a chart of operating characteristics of the system which facilitates an understanding of its operation. FIG. 6 is a chart of characteristic curves which facilitates an understanding of the operation of the spark-sensing device, and FIG. 7 is a simple schematic diagram of a power supply which may be used for supplying direct control voltage of appropriate magnitude.

General organization Referring now to the drawing and particularly to FIG. 1, an electrostatic precipitator is conventionally illustrated as comprising a grounded extensive sur-face collecting electrode 1 which may be in the form of a metallic tube, and fine wire discharge electrode 2 extending axially into the tube. These electrodes are provided with connections to a source of voltage which is represented by the alternating voltage supply conductors 3. These connections comprise a high voltage transformer 4 and a I grator.

Patented July 18, 1961 Kit? full wave bridge configuration rectifier 5 of which the input terminals 5a and 5b are connected to the secondary winding of the transformer and of which the direct voltage output terminals 50 and 5d are connected to the electrodes 1 and 2. The individual rectifiers of the bridge configuration are poled to provide positive polarity voltage at terminal 50 and negative polarity voltage at terminal 5d as indicated by appropriate polartiy markings. To terminals 6, 7 and 8, which constitute the input terminals of a spark-sensing device 9, are respectively connected the grounded collector electrode 1, the positive rectifier terminals 50 and the negative rectifier terminal 5d. A relatively high resistance 10 is connected between the terminal 8 and the negative terminal 5d. When the spark-detecting device 9, which is illustrated in detail in FIG. 2, is connected to the precipitator, the grounded collector electrode 1 is connected through a rheostat 11 to the positive rectifier terminal, and across the output of the rectifier 5 a high resistance path comprising resistors 10 and 12 in series is connected between terminal 7 and negative terminal 5d.

Included in the precipitator supply connections between the A.C. supply terminals 3 and the primary winding of the high voltage transformer is a suitable voltagevarying device. This voltage-varying device is illustrated in FIG. 1 as a saturable core reactor 13 which comprises a magnetic core member (not shown) upon which is mounted a D.-C. saturation control winding 13a and an A.-C. load circuit reactance winding 13b which is connected in circuit with the primary winding of transformer 4. The reactance of the A.-C. winding is maximum when the D.-C. saturating current is Zero and is minimum when the saturating current is maximum. For intermediate values of saturating current the reactance has corresponding intermediate values inversely related to the value of the saturating current.

The output of the spark-sensing device 9 is supplied to the input of an integrating device 14 which at its output produces a direct voltage which is the time integral of its input voltage and which has a polarity that is related to the sparking rate of the precipitator. Suitable switching means respond to predetermined magnitudes and polarities of this output voltage to complete the supply of an input voltage to a second integrating device 15 which produces at its output terminals direct voltages which are time integrals of the input voltage and which has the operating characteristic, upon subsequent removal of its input, of maintaining its output voltage at the attained integrated value. The output of integrator 15 is amplified by a suitable amplifier such for example as the magnetic amplifier 16 having input saturation control windings 16a and 16b connected to the output of the inte- The direct amplified output of the amplifier '16 is supplied to the saturation control winding 13a of the saturable reactor.

Control power supply Direct control voltages of appropriate magnitudes are furnished to the spark-sensing device, integrators and amplifiers from a suitable supply source 17. This supply is illustrated in FIG. 7 as comprising a constant voltage transformer 18 supplied from a suitable alternating voltage source such as the supply conductors 3, a bridge configuration full wave rectifier 19 supplied from the secondary winding 18a, resistors 2R, 3R, 4R and SR connected in series with a resistor IR and an adjustable rheostat IRA across the output terminals of the rectifier. The resistors of the voltage divider are approximately equal with the result that the voltage levels at terminals 21, 22, 23, 24 and 25 differ from each other by approximately equal increments. With the terminal 21 at zero voltage the rheostat IRA may be adjusted to produce a range of voltage levels such for example as volts, 50 volts, 75 volts and 100 volts at terminals 22, 23, 24 and 25 respectively. These values are selected as merely illustrative of a series of voltage levels which will provide satisfactory operation. Other voltage levels may be selected to provide equally satisfactory operation.

Spark-sensing device In FIG. 2 the spark-sensing device 9 is illustrated as comprising a two-stage transistor amplifier of which the first stage comprises an n-p-n type junction transistor 26 having its collector 26a. connected through resistor 27 to the 25 volt bus 22, its base 26b connected to grounded input terminal 6 and its emitter 26c connected to input terminal 8 and to zero volt bus 21. The second stage comprises an n-p-n transistor 28 having its collector 28a connected through a resistor 29 to output terminal 30 which is also the input terminal 30 of integrator 14 (see FIG. 3), its base 2812 connected through coupling resistor 31 to the collector of transistor 26 and its emitter 280 connected to an intermediate point 32 of a voltage divider comprising resistors 32A and 32B of which the voltage at such intermediate point is a few volts positive with respect to terminal 21. A capacitor 33 is connected in parallel with rheostat 11.

Briefly the spark-detecting device operates in the following manner: When no sparks are occurring in the precipitator the voltage of terminal 8 is so negative with respect to terminal 6 that transistor 26 is turned on. Consequently the voltage at its collector 26a is not sufficiently positive to turn on transistor 28 which therefore remains turned off. In FIG. 6 the voltage at ground terminal 6 is represented by the Zero ordinate line 34 and the voltage at terminal 8 is represented by the curve 35. Similarly the voltage at output terminal 30 with respect to 25 volt supply bus 22 is represented by curve 36. When a spark occurs in the precipitator as shown in FIG. 6 the voltage drop between the precipitator electrodes 1 and 2 vanishes with the result that the negative terminal 5d of the rectifier is elevated to ground voltage, and as shown in FIG. 6 the voltage at terminal 8 becomes sufiiciently less negative (or more positive) with respect to terminal 6 to turn off transistor 26. The resulting increase in voltage at collector 26a turns on transistor 28 with the result that the voltage of terminal 30 suddenly becomes more negative as represented by the steep vertical portion 36a of curve 36. When the spark terminates, the voltage of terminal 8 again becomes negative with respect to ground and the voltage at terminal 30' gradually decays to its initial value at a rate depending on the capacitor 37 and resistor 29. Thus assuming a condition of sparking in the precipitator which is represented by curve 35, the voltage at the input terminal of integrator 14 will be represented by curve 36.

Integrators As shown in FIG. 3, integrating device 14 comprises a plural stage transistor amplifier having single sided input and intermediate stages and a double sided output stage. The input stage comprises an n-p-n junction transistor 38 having its collector connected through a resistor 39 to the 75-volt bus 24, its emitter connected to 25-volt bus 22 and its base connected through resistor 40 to input terminal 30 and through a resistor 41 to the slider 42a of a rheostat 42 which is connected across buses 21 and 24. Similarly, the second stage comprises a transistor 43 having its base resistively coupled to the collector terminal of thefirst stage. A pair of emitter coupled p-n-p junction transistors 44 and 45, connected in unsymmetrical diiferential configuration with the base of transistor 44 resistance coupled to the collector terminal of transistor 43 and the base of transistor 45 connected to an intermediate voltage level bus e.g. to the SO-volt bus 23, comprise the ouput stage. The emitters 44a and 45a are connected to a common terminal and between this common terminal and the highest level voltage bus 25 is connected a resistor 46 which is thus common to both conducting paths of the output stage. Connected between the collectors 44c and 450 are two independent resistors 47 and 48 each approximately equal to the resistance 46. A characteristic of this configuration is that the currents in the two paths vary inversely and that the sum of the currents is approximately constant. The output is taken at the collector terminals 44d and 45d. From the output terminal 44d to the input terminal 30 of the first stage is provided a negative feedback connection in which is included a capacitor 42. When both paths of the output stage are conducting equally, the voltage at the output terminals is Zero. Under conditions of unbalanced conduction there appears across the output terminals a direct voltage of which the polarity depends on the direction of the unbalance. For a precalibrated position of the slider 42a, the first and second stage transistors 38 and 43 will be conducting just sufiiciently to effect balanced conduction in the output stage. A change of the voltage at input terminal 30 in the positive sense tends to turn on transistor 38, turn off transistor 43, turn off transistor 44 and turn on transistor 45. As a result the voltage at terminal 45d becomes increasingly positive and that at terminal 4411 becomes increasingly negative. If the voltage at input terminal 33' is changed in a negative direction, the voltages at these terminals change in the reverse sense. In either case the voltage across the output terminals rises at a rate which is determined by the magnitude of the input voltage and by the RC time constant of the feedback and thus the output voltage is the time integral of the input voltage.

Across the output terminals, in parallel circuit arrangement, are connected the operating coils 50a and 51a of switching devices 50 and 51 which are known as the raise and lower relays. In series with coil 50a is connected a rectifier 52 and in series with coil 531a is connected a reversely poled rectifier 53. At zero output voltage both coils are deenergizcd and both relays are dropped out. For any other value of output voltage one of the rectifiers will conduct and one of the coils will be energized while the other rectifier will act as a blocking rectifier and prevent energization of its associated coil. A normally open contact 5% serves when raise relay 50 is picked up to connect the input terminal 30 through a resistor 54 to the zero voltage bus 21 and a corresponding contact 51b serves when the lower relay 51 is picked up to connect it to the SG-volt bus 23 through a resistor 55. The rclays 50 and 5.1 are also provided with normally open contacts 50c and 510, which, when either relay is picked up, serve to complete the supply of voltage of appropriate magnitude to the input of the second integrator 15. Relays 50 and 51 modify the operation of integrator 14 as follows:

Application of a positive voltage at input terminal 3t? causes the output voltage which is positive at terminal 45d to increase at a predetermined rate. In response to a predetermined value of output voltage the raise relay responds to pick up and close its contacts 50b and Site. In closing, contacts 5% connect input terminal 30 through resistor 54 to the zero voltage bus 21 which is negative with respect to the emitter. This tends to turn ofi transistor 38 and as a result the output voltage begins to decrease at a predetermined rate which is determined by the magnitude of the input voltage and by the time constant of the feedback. At a predetermined lower value of output voltage the raise relay drops out and opens its contacts. This tends to turn on the input transistor 38 and as a result the output voltage begins to increase again and the operation just described is repeated.

The integrator 15 (see FIGS. 1 and 4) comprises a first stage transistor 56, -a second stage transistor 57 and a pair .of output stage transistors 58 and 59 which-are onn'ect ed in double-sided emitter-coupled unsymmetrical differential configuration. Output terminals 60 and 61 are included to provide for connection of turn-oft control winding 16a of the magnetic amplifier in one side of the output and turn-on winding 16b in the other side. The base of the input stage transistor 56 is connected to input terminal 62 and is also connected through a rheostat 63 to the 100-volt bus 25. The emitter of transistor 56 is connected to the slider 64a of a rheostat 64 which is connected in series with a resistor 65 across the zero volt and 25 volt buses 21 and 22. A capacitor 66 is included in a negative feedback connection between terminal 58a in the output stage and the input terminal 62. This capacitor is many times, e.g. times, as large as the feedback capacitor 49 of integrator 14.

Bias current in the input stage is required to bring the integrator 15 into operating range with equal currents in both sides of the output stage. This is accomplished by disconnecting the capacitor 66 and simultaneously adjusting the rheostats 63 and 64 to produce current conduction in both sides of the output with the voltage of the base of the input stage approximately equal to the voltage of supply bus 22. A very small change in base current of the input stage, e.g. a change of l microampere, will completely unbalance the output stage. If, when the output is unbalanced, all inputs are disconnected, the voltage at output stage terminal 58a will tend to change. However, a very low rate of change of this voltage e.g. volt per second will produce a current in the feedback circuit approximately equal to the value which produces complete unbalance of the output stage. Since the feedback is negative it thus effectively prevents any change in output. Actually there is a slow decay of the charge on the capacitor 66 which, after a long time, e.g. one hour, would permit the output stage to return to the balanced condition. For practical purposes, if the input is removed the output will remain unchanged.

Magnetic amplifier Although any suitable form of magnetic amplifier may be used, the magnetic amplifier 16 is preferably of the amplistat type. It comprises a magnetic core member (not shown) on which are mounted a pair of load circuit gate windings 67 and 68. These windings are connected in parallel arms of a bridge network which comprises four rectifiers 69, 70, 71 and 72 which are poled to provide full wave rectification at the output terminals 73 and 74 to which is connected the saturation control winding 13a of the saturable reactor 13. The input terminals are supplied from a suitable source of alternating voltage such for example as the supply conductors 3. Also wound on the core member of the magnetic amplifier are the turn-on control windings 16b and the turnofi control windings 16a which are connected in opposite output legs of the integrator 15.

Operation With the foregoing understanding oi the elements and their organization, the operation of the system itself will readily be understood from the following detailed description taken in connection with the graphs of characteristic curves 75 and 76 in FIG. 5. In this figure ordinates of curve 75 represent voltage applied to the precipitator electrodes and ordinates of curve 76 represent output voltage of integrator 14. Abscissae represent time. As an initial condition it is assumed that the output of the integrator 14 is zero as represented by the ordinate of curve 76 at time T-0. Under this condition, minimum voltage is applied to the precipitator as represented by the ordinate of curve 75 at time T-t) which results in a condition of no sparking. In the absence of sparking, terminal 8 of the spark-sensing device is negative with re spect' toterminal 7 of the spark-sensing device. This turns on the input stage and turns off the output stage so that no signal voltage is supplied to the input of the integrator 14. The slider 42a of the rheostat 42, being adjusted to supply a positive voltage to the input terminal 30 of the integrator, the voltage across the output terminal begins to increase at a predetermined rate, e.g. 5 volts per second as indicated by the portion of curve 76 between times T-0 and T1. During this period the voltage applied to the precipitator remains constant as shown by the horizontal portion of curve 75 between T-0 and T1.

At a predetermined value of output voltage which is represented by the ordinate of curve 76 at time T1, raise relay 50 picks up and closes its contacts. Contact 50b, in closing, connects the input terminal 30 of integrator 14 to the zero voltage bus 21 which causes the output voltage of the integrator to decrease at a predetermined rate as represented by the downward sloping portion of curve 76 between times T1 and T2. The contact 500 in closing connects input terminal 62 of integrator 15 to the zero voltage bus thereby unbalancing its output stage to cause the current in the turn-on winding 16b to increase and the current in the turn-off winding to decrease. This results in increasing the current in the control winding 13a of the saturable reactor which in turn increases the voltage supplied to the precipitator as represented by the upward sloping portion of curve 75 between times T1 and T2.

At a predetermined lower value of output voltage of the integrator 14 the raise relay 50 drops out and opens its contacts. Contact 500 in opening disconnects input terminal 62 of intengrator 15 'from the Zero voltage bus and, owing to the action of the negative feedback, the output of integrator 15 remains constant at the value which it had attained at time T2, the instant of opening of contact 50c. As a result, the voltage supplied to the precipitator ceases to increase but remains constant at the value which it had attained at time T2 as represented by the horizontal portion of curve 75 between times T2 and T3. Contact 50b in opening disconnects the input terminal 30 from the zero voltage bus 31 and the output voltage again begins to rise at the same predetermined rate as represented by the upward sloping portion of curve 76 between times T2 and T3.

In response to the integrator output voltage again attaining the predetermined pick up value at time T3 the raise relay 50 again closes its contacts 50b and 500. The closing of contact 500 initiates a further increase in the voltage applied to the precipitator as represented by the rising portion of the curve 75 between times T3 and T4, and the closing of contact 5012 initiates a decrease in output voltage of integrator 14 as indicated by the downward sloping portion of came 76 between times T3 and T4.

At time T4, the voltage applied to the precipitator reaches a value which for the conditions existing within the precipitator at that instant, is sufficient to cause an interelectrode spark. This causes a negative voltage to be applied to the input terminal 30 of integrator 14 with the result that the rate of decrease of output voltage is increased as represented by the increased steepness of the slope of curve 76 between times T4 and T5. The output voltage decreases to the drop-out value of the raise relay 50 at time T5. In response, the relay opens its contact 50c to stop the increase of voltage applied to the precipitator. This voltage now remains constant at its attained value as represented by the horizontal portion of the curve 75 at time T5. The opening of contacts 50b disconnect input terminal 30 from the zero voltage bus. However the output voltage continues to decrease, although at a decreased rate, owing to the decreasing voltage supplied to the input terminal 30 from the spark-sensing device. This is illustrated by the decreased slope of the portion of the curve 76 between times T5 and T6. At time T6 the spark signal vanishes and the output voltage of the integrator 14 again be- '7 gins to increase as represented by the upward sloping portion of the curve between times T6 and T7.

At time T7, owing to the continued application of high voltage and the conditions existing within the .preoipitator, another spark occurs. Again the spark-sensing device supplies a negative voltage to integrator 14 causing the integrator output voltage to decrease rapidly to zero, to reverse polarity and to increase in magnitude in the opposite sense as represented by the portion of the curve 76 between times T7 and T8. At time T8 the spark signal has decayed to zero to permit the integrator output voltage to decrease in magnitude, i.e. become less negative as represented by the portion of the curve 76 between times T8 and T9. Another spark occurs at T9 and the action described beginning at T7 is repeated except, of course, that the polarity of the voltage does not reverse.

The integrator output voltage continues to increase, i.e. become more negative until at time T10 it attains the predetermined value at which lower relay 51 picks up and closes its contacts 51b and 51c. In their closed position contacts 510 connect the input terminal 62 of integrator to the fifty volt bus v22'. This causes transistors 58 and 59 to increase the current through the oft control winding 16a and to decrease the current through the on control winding which results in decreasing the voltage applied to the precipitator electrodes as indicated by the downward sloping portion of curve '75 at time T10. Contacts 51b in closing connect input terminal to the positive supply bus 23 which causes the integrator output voltage rapidly to become less negative as indicated by the portion of the curve 76 between times 110 and "P11. Another spark occurs at time T11 and again the integrator output voltage becomes more negative. By time T12 the spark signal has decayed to zero and the output voltage again decreases, i.e. becomes less negative at a rapid rate owing to the combined influences of the positive voltages supplied from rheostat 42 and from positive bus 23 to input terminal 30.

At time T13 the integrator output voltage has decreased to the predetermined value at which lower relay 51 drops out and opens its contacts. Contact 510, in opening, disconnects the input terminal of integrator 14 from the zero voltage bus 21 to interrupt decreasing the voltage applied to the precipitator which voltage now remains constant at the decreased value which it has attained as represented by the horizontal portion of curve 75 at time T13. The opening of contact 51b disconnects input terminal 30 from the positive voltage bus 23. Consequently the integrator output voltage continues to become less negative but at a slower rate as indicated by portions of curves 76 at time T13.

Thus it is seen that the raise relay 50 picks up after a period of no sparking or infrequent sparking and causes -a higher voltage to be applied to the precipitator. Lower relay 51 picks up after a period of frequent sparking and causes a lower voltage to be applied to the precipitator. if the gases going through the precipitator remain constant, a sparking rate may be attained which will cause the integrator output voltage to remain approximately in the center of its range. When the content of the gases going through the precipitator changes the sparking rate will change. If the sparks occur more frequently the integrator output voltage will decrease and after a short time delay which is related to the sparking rate will cause the precipitator voltage to be reduced. If the sparks had occurred less frequently, this integrator output voltage would increase and eventually would cause more voltage to be applied to the precipitator. It will also be noted that the correction of precipitator voltage as represented by the sloping portions of curve 75 take place in a series of steps separated from each other by time intervals.

Although the invention .is .not limited -to particular 8 values of the resistors and capacitors utilized, the values set forth in the following tabulations have been found to produce satisfactory operation.

Resistors R megohms 150 ohms 56 K (thousand ohms 2 ruegohms ohms 1,800 ohms Capacitors: Microfarads 33 2000 37 4 49 S0 66 500 Although in accordance with the provisions of the patent statutes, this invention has beendescribed as embodied in concrete apparatus and the principle has been described together with the best mode in which it is now contemplated applying that principle, it will be understood that the invention is not limited to the specific apparatus shown and described since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of the invention or from the scope of the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A system for con-trolling the energization of the electrodes of an electrostatic precipitator having alternating voltage supply connections comprising voltage varying means included in said connections, an integrating device for producing a direct output voltage in response to a relatively high frequency of input pulses and a direct output voltage of opposite polarity in response to a relatively low frequency of input pulses comprising a source of control voltage, a network having an input connected to receive a control voltage from said source and an output, a device for sensing interelectrode sparks and supplying to said input, pulses derived from said sparks and of opposite polarity with respect to said control voltage, and a negative feedback connection from said output to said input including an energy storage device for causing said output voltages to vary at a predetermined rate and means responsive to said output voltage for causing said voltage varying means to increase or decrease the magnitude of the voltage of said supply connections in dependence on the polarity of said output voltage.

2. A system for controlling the energizationof the electrodes of an electrostatic precipitator having alternating voltage supply connections comprising voltage varying means included in said connections, a device for sensing and converting interelectrode sparks into voltage pulses, an integrating device for producing a direct output voltage in response to a relatively high rate of sparking and a direct output voltage of opposite polarity in response to a relatively low rate of sparking comprising, a source of direct control voltage, a network having an output and having an input connected to said source for receiving a direct control voltage of one polarity to cause said output voltage to increase in magnitude and for receiving from said spark sensing device voltage pulses of opposite polarity with respect to said control voltage to cause said output voltage to decrease in magnitude, a negative feedback including an energy storage device connected between said output and said input for causing said output voltage to vary at a predetermined rate and means responsive to said output voltage for causing said voltage varying means to vary the voltage of said supply connections in a sense dependent on the polarity of said output voltage.

3. A system for controlling the energization of the electrodes of an electrostatic precipitator having alternating voltage supply connections comprising voltage-varying means included in said connections, a device for sensing interelectrode sparks, an integrating device for producing a direct output voltage in response to a relatively high rate of sparking and a direct output voltage of opposite polarity in response to a relatively low rate of sparking comprising a network having an output and having an input for receiving a direct control voltage of one polarity to cause said output voltage to change in magnitude at a predetermined rate and for receiving from said spark-sensing device a signal voltage of opposite polarity to cause said output voltage to change in the reverse sense at a predetermined rate and means for causing the voltage of said supply connections to be varied in a succession of steps comprising switching means responsive to a first predetermined value of said output voltage to control said voltage-forming means to vary the voltage of said supply connections and to supply to said integrating, network a second control voltage to reverse the direction of change of said output voltage and responsive to a different predetermined value of said output voltage to discontinue said second control voltage and thereby temporarily to inten'upt the action of said voltagevarying means pending restoration of said output voltage to said first predetermined value at said predetermined rate.

4. A system for cont-rolling the energization of the electrodes of an electrostatic precipitator having alternating voltage supply connections comprising voltagevarying means included in said connections, a device for sensing interelectrode sparks, an integrating device for producing a direct output voltage in response to a relatively high rate of sparking and a direct output voltage of opposite polarity in response to a relatively low rate of sparking comprising a plural stage transistor amplifier having an output stage, an input stage for receiving a first direct control voltage to cause said output voltage to change in magnitude and for receiving from said sparksensing device a control voltage of opposite polarity to cause said output voltage to change in the opposite sense, and a negative feedback connection including a capacitor from said output stage to said input stage, and means responsive to said output voltage for causing said voltage varying means to vary the voltage of said supply connections in a sense related to the polarity of said output voltage.

5. A system for controlling the energization of the electrodes of an electrostatic precipitator having alternating voltage supply connections comprising voltagevarying means included in said connections, a device for sensing interelectrode sparks, an integrating device for producing a direct output voltage in response to a relatively high rate of sparking and a direct output voltage of opposite polarity in response to a relatively low rate of sparking comprising a plural stage transistor amplifier having an unsymmetrical diflerential double-sided output stage, a single-sided input stage for receiving a first control voltage to effect a change in magnitude of said output voltage and for receiving from said sparksensing device a control voltage of opposite polarity to eifect an opposite change in magnitude of said output voltage, and a negative feedback connection including a capacitor from one side of said output stage to said input stage, and means responsive to said output voltage for causing said voltage-varying means to vary the voltage of said supply connections in a sense related to the polarity of said output voltage.

6. A system for controlling the energization of the electrodes of an electrostatic precipitator having alternating voltage supply connections comprising voltagevarying means adopted to be included in said connections, a device for sensing interelectrode sparks, an integrating device for producing a direct output voltage of one polarity in response to a relatively low rate of sparking and of opposite polarity in response to a relatively high rate of sparking comprising a plural stage transistor amplifier having an output stage, an input stage for receiving a first control voltage to efiect a change in magnitude of said output voltage, and for receiving from said spark-sensing device a signal voltage of opposite polarity to effect an opposite change in magnitude of said output voltage, means for causing the voltage of said supply connections to be varied in a succession of steps comprising switching means responsive to a first predetermined value of said output voltage to control said voltage-varying means to initiate a variation of the voltage of said supply connections and to supply to the input stage of said integrating device a second control voltage to reverse the direction of change of said output voltage and responsive to a different predetermined value of said output voltage to discontinue said second control voltage thereby temporarily to interrupt the action of said voltage-varying means pending restoration of said output voltage to said first predetermined value, and means for controlling the rates of said changes in magnitude comprising a negative feedback connection including a capacitor from said output stage to said input stage.

7. A system for controlling the energization of the electrodes of an electrostatic precipitator having alternating voltage supply connections comprising voltage-varying means included in said connections, a device for sensing interelectrode sparks, a first integrating device having an output and having an input for receiving a first control voltage to produce an output voltage changing in magnitude at a predetermined rate and for receiving from said spark-sensing device a signal voltage of opposite polarity to cause said output voltage to change in magnitude in the opposite sense at a predetermined rate, and means for causing the voltage of said alternating voltage supply connections to be varied in a succession of steps separated by time intervals comprising a device responsive to a predetermined value of said output voltage to supply to said input a second control voltage opposing said first control voltage to cause said output voltage to change at a predetermined rate in the opposite sense and responsive to a dilferent predetermined value of said output voltage to discontinue the supply of said second control voltage thereby to terminate said opposite change in output voltage, a second integrating device having an output voltage which changes at a predetermined rate in response to an input voltage and which remains substantially constant at its attained value in response to interruption of the supply of input voltage, means responsive to said first predetermined value of output voltage to supply an input voltage to said second integrating device and responsive to said different predetermined value for interrupting the supply of input voltage to said second integrating device, and means responsive to the output voltage of said second integrating device for controlling said voltage-varying means to vary the voltage of said alternating voltage supply connections in predetermined relationship to the output voltage of said second integrating device.

8. A system for controlling the energization of the electrodes of an electrostatic precipitator having alternating voltage supply connections comprising voltagevarying means included in said connections, a device for sensing interelectrode sparks, a first integrating device having an output and having an input for receiving a first control voltage and for receiving from said spark sensing device a control voltage of opposite polarity to produce a direct output voltage changing in magnitude and having a polarity related to the sparking rate, and means for controlling said voltage-varying means to vary the voltage of said alternating voltage supply connections comprising a second integrating device having an output voltage changing in value in response to an input voltage and substantially retaining its attained value in response to removal of said input voltage, and means responsive to a predetermined value of the output voltage of said first integrating device for supplying an input voltage to said second integrating device and responsive to a different predetermined value thereof for discontinuing the supply of input voltage to said second integrating device.

9. A system for controlling the energization of the electrodes of an electrostatic precipitator comprising a device for sensing interelectrode sparks and deriving electrical pulses therefrom, a source of control voltage, an integrating device for producing a direct output voltage in response to a relatively high frequency of input pulses and a direct output voltage of opposite polarity in response to a relatively low frequency of input pulses comprising a network having an output and having an input connected to said source to receive a control voltage and connected to said spark sensing device to receive pulses of opposite polarity with respect to said control voltage, a negative feedback connection from said output to said input including an energy storage device for causing the magnitude of said output voltage to vary at a predetermined rate, and means responsive to a predetermined value of output voltage for changing the magnitude of the voltage of the electrodes in a sense dependent on the polarity of said output voltage and responsive to a relatively lower value of output voltage of either polarity for discontinuing the variation of said electrode voltage.

10. A system for controlling the energization of the electrodes of an electrostatic precipitator having alternating voltage supply connection comprising a saturable reactor having a reactance winding included in said connections and having a magnetization control winding, a device for sensing interelectrode sparks and deriving electrical pulses therefrom, a source of control voltage, an integrating device for producing a direct output voltage in response to a relatively high frequency of input pulses and a direct output voltage of opposite polarity in response to a relatively low frequency of input pulses comprising an amplifier having an output and having an input connected to said source to receive a control voltage and connected to said sensing device to receive pulses of opposite polarity with respect to said control voltage, a negative feedback connection from said output to said input including an energy storage device for causing the magnitude of said output voltage to vary at a predetermined rate and means responsive to a predetermined value of output voltage for varying the excitation of said control winding in a sense dependent on the polarity of said output voltage and responsive to a relatively lower value of output voltage of either polarity for discontinuing the variation of excitation of said control winding.

11. A system for controlling the energization of the electrodes of an electrostatic precipitator having voltage supply connections comprising voltage varying means included in said connections, a first integrating device for producing a direct output voltage in response to a relatively high rate of sparking and a direct output voltage of opposite polarity in response to a relatively low rate of sparking comprising a source of control voltage, a first network having an input connected to receive a control voltage from said source and an output, a device for sensing interelectrode sparks and supplying to said input, pulses derived from ,said sparks and of opposite polarity with respect to said control voltage, and a negative feedback connection from said output to said input including a first energy storage device for causing said output voltage to vary at a predetermined rate, means for controlling said voltage varying means to vary the voltage of said alternating voltage supply connections comprising a second integrating device having an output voltage which changes at a predetermined rate in response to an input voltage and which remains substantially constant at the value attained at the instant of interruption of the supply of input voltage thereto comprising a second network having an output, an input and a negative feedback therebetween including a second energy storage device of rel atively large capacity in comparison with said first energy storage device and means responsive to a predetermined value of the output voltage of said first integrating device for supplying an input voltage to said second integrating device and responsive to a different predetermined value thereof for discontinuing the supply of input voltage to said second integrating device.

References Cited in the file of this patent UNITED STATES PATENTS 2,741,104 Hall Aug. 17, 1956 2,841,239 Hall et a1. July 1, 1958 2,907,403 Foley Oct. 6, 1959 

